The technique of isolated rat liver perfusion developed in our laboratory has been adapted to the use of heterospecies "blood" consisting of bovine red cells suspended in Krebs Ringer bicarbonate buffer containing 3% bovine serum albumin. With this perfusion medium, initial perfusate levels of rat plasma proteins are very low and permit accurate specific serological measurement of net biosynthesis of rat plasma proteins during experiments routinely 12 or 24 hours in duration. Experiments to be conducted in vivo, and especially in the isolated perfused rat liver system will continue our study of factors regulating net synthesis of rat serum albumin, fibrinogen, alpha1-acid glycoprotein (Darcy, Gordon, Miller), alpha1-acid glycoprotein (Kawasaki, Jamieson), alpha2-(acute phase) globulin, haptoglobin, alpha2-U-globulin (male sex protein), and transferrin; they will be extended to include C3 component of complement hemopexin and ceruloplasmin. Factors to be further investigated include those acting in the liver donors; namely those associated with experimental tissue injury such as, sterile turpentine abscess, endocrine ablation and toxic agents (heavy metals, alcohol, drugs such as phenobarbital and colchicine). Factors to be evaluated for direct action on the liver in the course of perfusion with a continuous infusion of amino acids plus glucose (basal condition), will include the hormones, growth hormone, prolactin bradykinin, prostaglandins, F1 alpha, F2 alpha, E1, and E2. These will extend and supplement our completed observations on effects of the hormones insulin, cortisol, growth hormone, glucagon, triiodothyronine, ACTH, epinephrine, norepinephrine and acetylcholine. Indirect evaluation of the half lives of messenger RNA's of specific plasma proteins in terms of altered rates of synthesis during perfusion with actinomycin D is to be extended to include all of the above mentioned proteins. Specific solid immunoabsorbants have been prepared for the isolation of specific plasma protein polysome complexes for rat serum albumin, and for rat alpha 1-acid glycoprotein. These will afford a basis for quantitative measurement of mRNA-polysome complexes to be used in interpreting the possible role of mRNA in mechanism of actions of factors causing large quantitative changes in net synthesis of specific plasma proteins.